
Accession Number : ADA318886
Title : Near and FarField Acoustic Scattering through and from Two Dimensional FluidFluid Rough Interfaces.
Descriptive Note : Technical rept.,
Corporate Author : WASHINGTON UNIV SEATTLE APPLIED PHYSICS LAB
Personal Author(s) : Moe, John E.
PDF Url : ADA318886
Report Date : OCT 1996
Pagination or Media Count : 230
Abstract : Recent experimental results (F. E. Boyle and N. P. Chotiros, J. Acoust Soc. Am. 91, 26152619,1992; N. P. Chotiros, J. Acoust Soc. Am. 97, 199214,1995) reveal acoustic penetration from water into sandy sediments at grazing angles below the compressional critical angle in relation to the mean surface. These authors interpret their results to indicate the excitation of a Biot slow wave in the sediment. Another explanation is considered here. Modeling the ocean as a homogenous fluid and the sediment as a lossy homogenous fluid, computer simulations of these experiments based on analytical derivations in this work show that roughness of the watersediment interface causes propagation of acoustical energy from water into the sediment at grazing angles below the compressional critical grazing angle; these simulations indicate that the experimental results can be explained in terms of diffraction of an ordinary longitudinal wave. These simulations use an analytical expression for the timedependent mean square incoherent field scattered through (and from) a rough 2D fluidfluid interface that is derived in terms of the bistatic scattering cross section per unit area per unit solid area (differential cross section) of the rough interface. Firstorder perturbation theory is used to derive an expression for the differential cross section. The coherent field is calculated using the flatsurface result (zeroorder perturbation theory) and compared to the coherent component of the secondorder perturbation theory result. Effects of soundspeed gradients on the field scattered from the rough watersediment interface are also shown using the firstorder perturbation derivations.
Descriptors : *ACOUSTIC SCATTERING, COMPUTERIZED SIMULATION, SIMULATION, ANGLES, PROPAGATION, INTERFACES, WATER, ACOUSTIC WAVES, COHERENCE, FAR FIELD, SURFACES, INCOHERENCE, PENETRATION, DIFFRACTION, PERTURBATION THEORY, FLUIDS, LOSSES, MEAN, OCEANS, ACOUSTIC VELOCITY, ROUGHNESS, SEDIMENTS, SLOW WAVE CIRCUITS, GRADIENTS, HOMOGENEITY, BISTATIC RADAR, DIFFERENTIAL CROSS SECTIONS, GRAZING ANGLES.
Subject Categories : Acoustics
Distribution Statement : APPROVED FOR PUBLIC RELEASE